Water Leak keeps coming back

My son has a 2000 Regal GS. Earlier this last summer he had water on the passenger floor. I searched and read several postings in here, so we replaced the cabin air filter when we checked the weather strip and cowling. I cleaned the weather strip (it was off) and used weather strip adhesive to reattach it. It has been a monsoon in Ohio and it has leaked again. He checked the weather strip and it is still in place. The flap was funtioning (and closed) when we fixed the weather strip. Is it possible the cowling is a little loose and allowing water in? He is in college so it is hard to fix it or verify things without him bring the car home. However he helped me the last time and checked the weather strip before calling me. It isn't AC type weather and he has a lot of water on the floor. Is there anything else that could be causing this? Something we could have reassembled wrong?

Does the car have a sunroof? One of the sunroof drains runs down the passenger a-pillar.

Yes it does have a sunroof. Can I take a air nozzle and blow this out or has something cracked or disconnected? Where does the bottom of the drain come out? What is the drain line made of metal or plastic?

Thanks in advance!